Helga Schiff

STRUCTURE AND OPTICS OF OMMATIDIA FROM EYES OF STOMATOPOD CRUSTACEANS FROM DIFFERENT LUMINOUS HABITATS

Shapes and sizes of ommatidia in six genera of stomatopods from different luminous habitats are described. Cornea-cone apertures and acceptance angles have been calculated. The ommatidia belong to the apposition type with fused rhabdoms as in most Malacostraca, but the spindle-shaped cone and the transparent wedges under the cornea are acquisitions of stomatopods. The same is true for rhabdom specializations, especially the thin undulated rhabdoms in ommatidia of the six-row middle band of the Gonodactyloidea, that divides the eye in two halves. Several regions can be distinguished in stomatopod eyes by differences in shapes, sizes, and proportions of their ommatidia and by the skewing pattern along the columns of ommatidia. As more light becomes available in the habitat, apertures and acceptance angles seem to decrease mainly by increasing the lengths of the cones.

CORNEA SHAPE AND SURFACE STRUCTURE IN SOME STOMATOPOD CRUSTACEA

ABSTRACT Three types of eyes have been observed in three different lineages of the Stomatopoda. In the Gonodactyloidea and the Squilloidea, the cornea is divided into two halves by a line of specialized ommatidia, the middle band. This band is two facets wide in the squilloids, and occupies a small portion, about 4 per cent, of the surface area of the cornea. In gonodactyloids the band is six facets wide and occupies much more of the surface area of the cornea, between 15 and 38 per cent. The middle band appears to be absent in the bathysquilloids. The greater development of the middle band in the gonodactyloid lineage than in the other lineages may be related to binocular vision and the strike of the raptorial appendage, light available in the habitat, and/or the complex behavioral patterns developed by some members of this group.

Possible monocular range-finding mechanisms in stomatopods from different environmental light conditions

Abstract 1. 1. Stomatopods have double eyes. 2. 2. In the middle band dividing the two halves of the eye ommatidia are perpendicular to the cornea. 3. 3. Rows of ommatidia parallel to the middle band have divergent optical axes. 4. 4. In the columns across the middle band the optical axes of ommatidia near the middle band are convergent between the two halves of the eye. 5. 5. From the fifth to tenth ommatidium towards the sides optical axes on each side are parallel to each other and to those in the middle band. 6. 6. This results in a strong overlap of visual fields between ommatidia with parallel optical axes in each half of the eye and with the fields of the skewed ommatidia from the opposite half of the eye. 7. 7. We postulate this as the morphological basis for a range-finding and motion measuring device along the columns, repeated around the eye along the rows. 8. 8. We hypothesize that this device may measure distances by the amount and pattern of overlap of visual fields at each point in space. 9. 9. Species from bright light habitats show less skewed ommatidia and similar patterns of overlap are shifted to longer distances than in dim light species.

Optical and neural pooling in visual processing in crustacea

Abstract 1. 1. Optical pooling is common in crustacean vision, both pooling in the single ommatidium and pooling inputs from many ommatidia by overlapping visual fields. 2. 2. Optical and neural pooling work together subdividing the eye into different surface regions with different tasks. 3. 3. Small-fiber and large-fiber systems with corresponding small and large dendritic branching provide a parallel processing system. 4. 4. Several parallel, integrating channels process that visual information which is needed for high-speed reactions. 5. 5. Visual fibers receive contributions from other modality inputs like vibration, olfaction or attention neurons. Inputs from mechanoreceptors transmitted over integrating fibers seem to join the signals in the intergrating visual fibers. 6. 6. The signal for a particular channel is expressed by the pattern of spikes (rather than changes in the mean frequency of spikes) which is modulated by any input variation. 7. 7. A particular discharge pattern may then be recognized by a command neuron or a muscle ensemble.

Modulation of spike frequencies by varying the ambient magnetic field and magnetite candidates in bees (Tapis mellifera)

1. Spontaneous activity was recorded from neurons in the second abdominal ganglion of bees. 2. Thirty per cent intensity modulations of the horizontal component of the background magnetic field provoked changes in the firing pattern of single neurons. 3. Two classes of neurons were distinguished and confirmed by statistical analysis. 4. Electron dense material in hairs and in or near the cutex may be single domain (SD) and superparamagnetic (SPM) magnetite. 5. A hypothesis is proposed for magnetoreception. Magnetite would act as an amplifier of the external magnetic induction changes. 6. The amplified magnetic field would influence neuronal elements only in restricted regions near the magnetite.

An Attempt to Correlate Pseudopupil Sizes in Stomatopod Crustaceans with Ambient Light Conditions and Behavior Patterns

Abstract 1. 1. The distribution of pseudopupils in the eyes of representatives of five genera of Stomatopoda has been studied. 2. 2. A triple pseudopupil is seen when the eye is viewed perpendicularly to the specialized middle band on the cornea, but a double pseudopupil appears when the direction of viewing is moved five degrees away from the vertical, as a result of the skewing of ommatidia adjacent to the middle band. 3. 3. Skewed ommatidia near the middle band constitute a monocular range-finder. 4. 4. Species with the most complex behavior patterns have the most complex skewing patterns of ommatidia.

Superposition and scattering of visual fields in a compound, double eye—II. Stimulation sequences for different distances in a stomatopod from a bright habitat

Abstract 1. 1. Inputs have been plotted for a point light source moving in front of a column of ommatidia. 2. 2. Visual fields overlap strongly in each half and between the two halves of the eye. 3. 3. Pattern of overlap changes with distance. 4. 4. Stimulation is continuous for sequences of ommatidia in each half of the eye. 5. 5. Spike pattern in a lamina fiber matches the computer histograms. 6. 6. The lamina contains a fiber with a horizontal-vertical distribution. 7. 7. We hypothesize an integrative mechanism for evaluation of distance and speed of a stimulus which translates the input pattern into a spike pattern.

A model for the dynamic properties of integrating fibers: Target localization in a three-dimensional space—I. Mathematical description

Abstract 1. 1. A mathematical model was developed based on the assumptions that information is processed in parallel channels and that high-speed channels work as integrators. 2. 2. Our model considers a luminous point moving in front of and in the plane of a two-dimensional sequence of ommatidia at different distances from the eye. 3. 3. The output of the array of phototransducers is formulated mathematically as the sum of gaussian curves which builds up as a function of the position of the point at each instant. 4. 4. The transfer function describes the transmission of electrical signals through the neurocartridges to the integrating fiber, a tangential fiber on the lamina surface. 5. 5. An impulse function shows a spatio-temporal pattern coding corresponding to the input conformation. 6. 6. The model suggests a new principle of stereo and motion vision based on analog, continuous and pattern-dependent processing.

Visual input patterns correlated to behavior and habitat of the mantis shrimp Gonodactylus

Abstract 1. 1. The disposition of ommatidia and optical axes in the eye of Gonodactylus is described. 2. 2. The matrix of horizontal and vertical fibers on the distal lamina surface presumably sub- serves integration of a complex input pattern and transmits signals for the strike to the raptorial appendages. 3. 3. The antennal scales contain two parallel nervous systems contributing apparently to the visual inputs for the strike. 4. 4. Some aspects of visual behavior correlated to the strike are reported. 5. 5. Computer simulations show the input patterns for points and segments moving around the eye in space. 6. 6. The patterns change with distance, size, speed and position of the target. 7. 7. It is hypothesized that the fiber matrix in the lamina integrates inputs and translates them into spike discharge patterns. The shape of the histograms, representing the patterns, contains the information necessary for catching a prey. 8. 8. The input pattern and its variations are correlated to the behavior, the histological results and the luminous habitat of the animals.

An introductory survey of ecology and sensory receptors of tropical eastern pacific crustaceans

Abstract A comparative survey of sensory organs (mainly visual) of 35 species of crustaceans (Mysidacea, Stomatopoda and Decapoda) was initiated in the SE Gulf of California, Mexico, an enclosed sea which has been well studied for its physical conditions and the taxonomy of crustacean species. The purpose of this survey was to study how the perceptive capacities are conditioned by the signals arriving from their environment. Studied species were sampled from terrestrial, intertidal, subtidal and deep sea habitats. Our data indicate that down to 200 m there seems to be not much difference of skewing patterns in stomatopods. Eyes are adapted to local conditions. In crabs and stomatopods, ommatidia are aligned in a vertical array along the longer axis of the eye. Visual fields of ommatidia overlap. This could emphasize, for instance, the horizontal motion of vertical edges. Deep‐sea crustaceans still have eyes, but in the same habitat species with apparently functional eyes occur together with species with s...